There are a few ways to install a kext (kernel extension). One of them is in L/E (Library/Extensions) or S/L/E (System/Library/Extension). And there are a few ways to accomplish that, as well. The other, and possibly the best one, is through Clover Bootloader itself (simply copy-pasting the kexts themselves in Clover/kexts/Other).

And I'll try to cover all of them to the best of my knowledge

1. Clover Bootloader method (recommended).

Note: this method might not work for all the kexts, but it should work for 99% of them. For example, CodecCommander and AppleBacklightInjector need to be installed in S/L/E. So if that's what you're trying to install, skip to the next method.

With this method, all you need is to mount your EFI partition (you can use Clover Configurator for that), navigate to EFI/EFI/Clover/kexts/Other and simply copy-paste all the kexts in here. That's it.

Reboot to see the changes.​

2. Terminal methods

Put the kext(s) on your Desktop (for easy access). It can be anywhere else, as long as you navigate to that location from Terminal. For the sake of simplicity, we'll assume the kexts are on your Desktop and we're trying to install CodecCommander.kext in S/L/E. If you're trying to use a different kext or you have it stored in another place other than Desktop, you'll have to update the command below accordingly​